i need help determining z values with a temperature change
i have a client who mfg a salad dressing with a ph of 3.0 and CCP is less than 3.5
he heats with the current process to 200F and holds for 5 minutes , cools and hot fills at 180F and inverts for 2 minutes
how would Z values compare if he reduces heat to 195F and holds for 1 minute , then hot fills at 180F
is there software to compare heat treatments to themal death rate to maintain 5 log reduction ?
Not really my area but I deduce from IT that -
"salad dressing" may be FDA regarded as an acid food rather than an acidified one.
The crude F(T,z) lethality values for each stage (assumed to refer constant, coldest temp. point ) can be calculated as per analogous formula to that in this attachment -
Lethality calculation.doc 79.5KB
Strictly you will need appropriate z-value.
The "121"/z values should, i think, preferably be referenced to a level close to yr pasteurizing temperature (eg.90degC). Maybe can try z= 10 for both temps in degC just to get an idea. Then add the 2 stages together.
Conservatively, could calculate for 1st stage only, eg ca. (5).[10 ^((93.3-90)/10)] = 10.7 for 1st option. Similarly > 1.12 for 2nd option.
And yes, excel programs for F are available and posted on this forum (somewhere). Particularly developed for temperatures not constant.
The above calculation compares yr applied F values.
Afaik the Z value itself is based on the applied lethality achieving a typical 5log bacterial reduction of species XYZ so may/may not be satisfied by the F values above.
This "validation" step requires a further calculation to determine No.of log reductions of XYZ achieved.
(In practice, i believe Z- "least sterilization values" may have additional safety factors built in also).
So the final step probably requires your specifying a relevant XYZ species, eg L.monocytogenes, determining (searching for) its appropriate D (Decimal Reduction) value for the food matrix involved, and applying one more calculation.
PS - this ref. contains recommended heat processing time/temperature combinations for a 5-log reduction in bacterial pathogens for acidified products with a pH of 4.1 or below -
Thermal processing of acidified foods, 2010.pdf 154.51KB
An additional table was issued in a Draft FDA document (2010) -
Thermal Process Lethalities for Safe Acidified Foods,2010.doc 47.5KB